PNY 6600-cooling questions

Hey whatsup, I just threw a vga water block on my pny 6600 256mb agp(non-gt) and when i was taking the stock fan off i took off the aluminum heatsink that was behind it to see what that chip was under it. well to get to the real question... that heatsink gets real damn hot and was wondering what that chip was before i start o/c'ing the card even more. Currently i am clocked in at 385/560 from 300/500. I'm really just trying to figure out what that other chip is and if its cool for me to try to get this card to about 400-410 at the core and maybe a lil higher on the memory. It would be greatly appreciated if you guys could help me out with this, i've looked all over the web to try and find out what it is and I figured the o/c'n gurus on here could help a brother out! thanks

I've got my 6600 clocked at 420 core/600 mem, temps run 56c idle to 71-72C load. Still air cooled with stock fan, but with AS5 applied on both fan and other heatsink. Couldn't really tell you how high to expect to go, just as long as you get no artifacts and temps stay ok.

I've no idea what's under the 2nd heatsink. Now that you mention it I'm kinda curious myself.